This invention relates to a reflecting optical system suitable to be used as, for example, an optical system in a projection-type exposure apparatus, more particularly, in an alignment and exposure apparatus for manufacturing large scale integrated circuits, etc.
There have already been proposed various types of reflecting optical systems for use in the alignment and exposure apparatuses. For example, one comprises a concave mirror and a convex mirror which are disposed concentrically or eccentrically. Another reflecting optical system comprises a concave mirror and a convex mirror disposed substantially concentrically with each other and includes a meniscus lens and a chromatic aberration correcting mechanism.
In these reflecting optical systems for the alignment and exposure apparatuses, a superior imaging region is defined in an arcuate area spaced from the optical axis. An image of a part of a mask corresponding to the superior imaging region is formed on a wafer while, on the other hand, the mask and wafer are moved as a unit relative to the reflecting optical system so that the mask and wafer are slit-scanned whereby the image of the entire mask is formed on the wafer. In such reflecting optical systems, however, the width of the superior imaging region (the width of the scanning slit) is very narrow, for example of the order of 1 mm. Therefore, when they are applied to the alignment and exposure apparatuses, a longer scanning time, that is, a longer exposure time is required which results in a lower throughput of the wafer exposure per a unit time period.